Thermionic gas-filled rectifier



Patented July 4:, 1&50

UNITED STATES 6F F ICE 2,514,165 THE'RM'IONIC GAS-FILLED RECTIFIER Henry ThcmasjRamsay, Hatch End;England, as-

signor toThe M-O Valve Company Limited,

London, England 1944, Serial No. 529,801.

vember 5, 1941 In Great Britain No- Section 1, Public Law 690, August 8; 1946 Patent expires November 5, 1961 9: Claims. 1

This invention relates to circuit arrangements comprising a thermionic gas-filled rectifier of the type wherein the cathode is separated from the anode by a labyrinth, wherein the rectifier has a control electrode separate from th cathode and the anode, and wherein the main discharge (1. e. that between cathode and anode) is started by making the control electrode so much positive to the cathode that a subsidiary discharge passes between those electrodes, and produces ions in such a position and in such an amount that they enable the main discharge to start.

It is important to distinguish circuit arrangements of this type from those wherein the rectifier is of the kind in which th 'function of the grid is substantially the same as that of the control grid in a vacuum, namely to co-operate with the anode in establishing at the surface of the cathode a field sufiiciently great to permit a large proportion of the electrons emitted from the cathode to leave the neighbourhood of the cathode. Accordingly the foregoing description of my improved type will be explained further.

The term labyrinth is defined as a construction arranged so that the starting of an ionforming discharge from the cathode is substantiall independent of the potential difference be tween anode and cathode. A necessary condition for such independence is that no straight line can be drawn from anode to cathode that does not intersecta conductor that is negativ to the anode during the starting period. A straight line passing through an aperture in a grid is not to be held to intersect the grid. But this condition is not suffioient. A suiiicient condition is that, if the anode and cathode potential is held constant and the control electrode is made progressively more positive to the cathode, the potential of the control electrode at which an ionforming discharge first occurs (evidenced by a Very sharp rise in th current between control electrode and cathode) is substantially independent of the anode-cathode potential. This proves that the anode and control grid do not co-operate in the starting of the first ion-forming discharge. The anode potential is effective only in converting this first discharge into a discharge between anode and cathode in virtue of the introduction of ions into the labyrinth.

It may be noted also that the two types differ greatly in the power that has to be supplied in operation to the control electrode. In the type in which the control grid operates as the control grid of a vacuum triode, the power has to be suficient only to raise the potential of the control 2 grid; it is determined by the capacities of the electrodes and is generally of the order of 1a milliwatt. Inthe type to which the invention relates the power supplied has to be sufiicient to provide an ion-forming discharge and generally is of the order of a watt.

In circuitarrangements of the type specified there must be efiicient deionisation of the labyrinth in the interval between two main-discharges. An object of this invention is to provide in circuit arrangements of this type means for promoting such-deionisation.

The electrode that is bombarded by positive ions during the deionisation period will sputter to some extent. Any sputtered matter that reaches the cathode will tend to impair its efiiciency. The life ofv the cathode may bemaintained at a reasonable value by limiting the negative potential imposed on-the bombarded electrode or the positive ions flowing to it, and thus limiting the sputtering. But then the deionising efiect of that electrode is also limited. A further object of the invention is to provide means for preventing much of' the sputtered material from reaching the cathode.

Another object of this invention is to provide improved gas-filledv thermionic rectifiers capable of use in the improved circuit arrangements.

Further objects and advantages of the inventionwill'be' apparent from the following description of three embodiments thereof, given by way of example with reference to the accompanying drawings, in which:

Figures 1 and 2show'respectively the relevant parts of two difierent rectifiers in axial section, together with certain circuit elements represented diagrammatically, and

Figure 3 showsa modifiedcircuit arrangement capable of use with the rectifier shown in Figure-2.

In'the rectifier shown in Figure l, the same structure servesboth as the control electrode and as the:auxiliaryxelectrode that operates to withdrawapositive ions from-the'labyrinth. Reference character I is the cathode, 2" the anode, 3 is a canister or cathode tube surrounding the cathode and connected thereto. The auxiliary or control electrode is made up'of a canister or tubel round the anode, a'tube 6, and a plate 5 spaced from and covering the end of the tube 5 within the canister or tube 4: the parts it, t are electrically connected together, and are maintained normally negative tothe cathode by abiassource 7 acting through a choke 8 and a lead l3. The plateli acts-as a bailieand is the main operative element of the labyrinth forcing the electrons to follow a circuitous path in traveling from the cathode to the anode; it shields the cathode completely from the potential of the anode. The construction as described is such that the anode 2 and control electrode 46 on the one hand and the control electrode 46 and cathode tube 3, on the other, telescope respectively the one with the other.

The current to be rectified is applied to the lines L, L and to start the discharge, a pulse of positive potential, generated from a source 9 of any of the types known in the art, is applied to the control electrode 4 through a resistor It; the choke 8 prevents the short-circuiting of the pulse through the battery. An ion-forming discharge is thus started between the cathode and that electrode, the current being limited by the resistor Hi. The ions produced by this discharge extend into the potential field of anode 2 and enable the main discharge to flow from the anode around the edge of the plate 5 and through the tube 6. When the discharge has been extinguished by reduction of the potential at the end of the c cle, the timing is such that the pulse is removed and the control electrode 4 is therefore negative and collects the residual positive ions. There is nothing to prevent matter sputtered from the parts 5 and 5 in Fig. 1 from reaching the cathode; consequently it will be understood that the negative potential at which they may be maintained is limited.

To aid in starting the discharge additional starting electrode [4 is provided but it may be omitted if desired.

In Figure 2, the numerals I, 2, 3, 4, 5, l, 3, i3 represent parts corresponding to those similarly denoted in Figure l; but there is no tube 6 projecting into the cathode tube 3. On the under side of the plate 5 is a plate H insulated from it. This plate, which serves as a baffle, is connected to the control electrode 4 by a resistor 82 to a point on which, intermediate between its end, the pulse generator 9 is connected.

The discharge is started as before by a pulse from 9 making 4, 5, and H all positive. The ions produced in the vicinity of the electrode l I are within the potential field f anode 2 and therefore the main discharge between the anode 2 and cathode l starts. When the main discharge is extinguished, the full deionising current can flow to the control electrode 4 and the plate but material sputtered from them is prevented from reaching the cathode by the plate ll. On the other hand the plate H has the resistance l2 in series with it, and the deionising current to it is limited so that there is no objectionable amount of sputtering from ions landing on it. Of course the deionisation is less rapid inside the cathode tube 3 than inside the control electrode 4; but so long as deionisation is sufiicient somewhere in the path through the labyrinth between anode and cathode the desired result is achieved.

Figure 3 shows a modification of the circuit of Figure 2. In this modification the parts 4, 5

= are always negative; the positive pulse is applied by the pulse generator 9 to the plate ll, which acts as the control electrode, through the resistor IZA. In this arrangement more power has to be supplied by the generator 9 in order to start the discharge. The electrodes of the rectifier are enclosed in a gas filled envelope 15 as usual. The envelope is shown only in Figure 1 but it will be understood that it will be used with the rectifiers of Figs. 2 and 3.

This application is a division of my prior appli- 4 cation, Serial No. 466.651, filed November 23, 1942, for Circuit Arrangements Comprising a Thermionic Gas-Filled Rectifier.

I claim:

1. A thermionic gas filled rectifier tube comprising a thermionic cathode, a cathode tube surrounding and connected to said cathode, a control electrode and an anode positioned in succession along the axis of the rectifier, said control electrode consisting of a conducting tube open at both ends one end of which surrounds said anode, an imperforate conducting plate Within said control electrode and connected thereto and extending almost completely there across, the other end of the conducting tube and one end of the cathode tube being telescoped one within the other and. spaced apart to provide a labyrinth forming a circuitous discharge path between said anode and said cathode.

2. A thermionic gas filled rectifier comprising a thermionic cathode, a cathode tube surrounding and connected to the cathode, a control electrode and an anode positioned in succession along the axis of the rectifier, said control electrode consisting of a conducting'tube open at both ends and having a conducting plate within and connected thereto and extending almost completely there across, said anode extending into one end of the conducting tube and spaced therefrom, the other end of the conducting tube extending into said cathode tube and spaced therefrom to provide a labyrinth foLming a circuitous discharge path between the anode and cathode.

3. A thermionic gas filled rectifier comprising a thermionic cathode, a cathode tube surrounding and connected to the cathode, a control electrode and an anode arranged in succession along the axis of the rectifier, said control electrode consisting of a conducting tube open at both ends and having a conducting plate within and connected thereto and extending almost completely there across, said anode and said control electrode having their adjacent ends telescoping one within the other and spaced apart, the other end of the conducting tube and one end of the cathode tube being telescoped one Within the other and spaced apart to provide a labyrinth forming a circuitous discharge path between the anode and cathode, and a bafile electrode having a separate terminal connection interposed between the oathode and the conducting plate to mask said cathode from said plate.

4. A thermionic gas-filled rectifier comprising a thermionic cathode, a control electrode tube and an anode arranged in succession along the axis of the rectifier, a cathode tube around said cathode having an opening facing said anode, one of said tubes having an end telescoping within the other in spaced relation and an imperiorate conducting plate connected to and Within the control electrode tube, said plate being of larger diameter than said telescoping end to provide a circuitous path between said cathode and said anode.

5. A thermionic gas-filled rectifier comprising a thermionic cathode, a control electrode tube and an anode arranged in succession along the axis of the rectifier, a cathode tube around said cathode having an opening facing said anode,

-' one of said tubes having a reduced end portion telescoping within the other in spaced relation and an imperforate conducting plate connected to and within the control electrode tube, said' plate being of larger diameter than said reduced end portion, and being spaced from said control electrode tube at its periphery to provide a, circuitous path between said cathode and said anode.

6. A thermionic gas-filled rectifier comprising a thermionic cathode, a control electrode and an anode arranged in succession along the axis of the rectifier and a tubular shield around said cathode having an opening facing the anode, the control electrode consisting of a conducting tube open at both ends, and having a portion of smaller cross-section extending into the said opening and spaced from said shield and a portion of larger cross-section extending towards the anode, said control electrode having a conducting plate Within the said portion of larger cross-section and extending thereacross to overlap the said portion of smaller cross-section, said anode extending into the open end of the said portion of larger cross-section and spaced from the sides thereof.

7. A thermionic gas-filled rectifier comprising a thermionic cathode, a control electrode tube and an anode arranged in succession along the axis of the rectifier, a cathode tube around said cathode having an opening facing said anode,

one of said tubes having an end telescoping within the other in spaced relation and an imperforate conducting plate connected to and within the control electrode tube, said plate being of larger diameter than said telescoping end to provide a circuitous path between said cathode and said anode, and a baflie plate of larger diameter than said telescoping end between the first mentioned plate and the cathode.

8. A thermionic gas-filled rectifier comprising a thermionic cathode, a control electrode tube and an anode arranged in succession along the axis of the rectifier, a. cathode tube around said cathode having an opening facing said anode,

one of said tubes having a reduced end portion telescoping within the other in spaced relation imperforate conducting plate connected to and within the control electrode tube, said plate being of larger diameter than said reduced end portion and being spaced from said control electrode tube at its periphery to provide a circuitous path between said cathode and said anode, and a baflle plate of larger diameter than said reduced end portion between the first mentioned plate and the cathode.

9. A thermionic gas-filled rectifier comprising a thermionic cathode, a control electrode, an anode, said control electrode further comprising a de-ionising electrode lying in the main discharge path between the cathode and anode, and a baifie electrode having a separate terminal connection interposed between the said de-ionising electrode and the cathode to mask it therefrom.

HENRY THOMAS RAMSAY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,942,080 Young Jan. 2, 1934 2,145,088 Kobel Jan. 24, 1939 2,206,008 Spencer June 25, 1940 2,227,747 Clark Jan. 7, 1941 2,227,829 Hansell Jan. 7, 1941 2,297,721 Smith Oct. 6, 1942 FOREIGN PATENTS Number Country Date 478,798 Great Britain Jan. 25, 1938 541,919 Great Britain Dec. 17, 1941 544,831 Great Britain Apr. 29, 1942 

